The long term goal of this research is the understanding of the mechanisms by which RNA tumor viruses cause malignant transformation of cells. The specific aim is to elucidate the genetic structure of these viruses. Three objectives are the goal of the present research proposal: 1. The generation of a coarse genetic map of avian sarcoma viruses. 2. The investigation of the genetic region responsible for transformation. 3. The investigation of models of provirus formation and recombination. It is anticipated that the application of genetics techniques to the study of RNA tumor viruses will elucidate several aspects of the problems of malignant transformation caused by these agents in animals and possibly in man.